Answer:
At least 7 shirts would need to be sold to cover their costs
Explanation:
Cost of producing x t-shirts.
The cost of producing x t-shirts is a flat fee of 35 plus 4.25 per t-shirt. So

Earnings of selling x t-shirts:
Charges $10 per t-shirt, so it earns 10 for each t-shirt it sells.

How many shirts would need to be sold to cover their costs?
To cover the costs, we need that the earnings are equal or higher than the costs. So





Since we cannot sell a decimal part of a shirt, at least 7 shirts would need to be sold to cover their costs